Cultures containing mammalian cells provide useful information in diagnostic virology studies and on the cytotoxicity of chemicals, pharmaceuticals, and materials. Cultures of these cells are also important for diagnostic genetics, such as when the genetic material of the cells is examined for chromosomal abnormalities during karyotyping. In another application of diagnostic genetics, amniocentesis, fetal cells are extracted from amniotic fluid, cultured, and processed for chromosome analysis.
These studies variously involve cell growth, incubation, immunodiagnostic testing, or other processing often including transfer of cells to a microscope slide. Many of these procedures require or benefit from centrifugation. See, e.g., Gleaves, C. A.; Wilson, D. J.; Wold, A. D.; and Smith, T. F., "Detection and Serotyping of Herpes Simplex Virus in MRC-5 Cells by Use of Centrifugation and Monoclonal Antibodies 16 Hours Postinoculation", 21 J. Clin. Microbiol. 29-32 (1985).
Presently, mammalian cells are grown in a variety of culture tubes, flasks, and petri dishes. Anchorage-dependent cells which must attach to a non-toxic substrate during growth are typically grown in culture tubes. Each conventional culture tube, however, exhibits one or more limitations during determination of cell viability and the subsequent testing, treating and processing required in cytological studies, particularly infectious disease diagnostic studies. In one such apparatus, a 16.times.125 mm glass tube with screw cap closure, cells are grown directly on the curved surface of the tube when it is placed horizontally. The curved surface renders microscopic examination quite difficult since only a fraction of the microscopic field is in focus at any one time. Further, the side of the tube presents a large culture surface which requires both large quantities of reagent and a great deal of time to examine. The shape of the tube renders it incompatible with a fluorescent microscope; the cells must therefore be scraped and transferred to a microscope slide. This procedure is time consuming and destroys the integrity of a monolayer culture, which particularly hinders cost-effective and reliable confirmation analysis for viral antigens.
Another culture system, the Ambitube, available from Flow Laboratories, is similar to the glass tube except that one of its sides is flattened to serve as the bottom and the tube is made of plastic. The Ambitube shares many of the disadvantages of the glass tube, including a large culture surface requiring time-consuming examination and large volume of reagents and a shape that is unsuited for a fluorescent microscope.
The Leighton tube, available from Costar, is also a horizontal culture system with a flattened side. It is plastic and contains a 9.times.55 mm paddle-like plastic insert on which cells are grown. The insert is often warped and rarely lies uniformly along the flattened side, making it difficult to examine the cells: the varying distance alters the focal plane and therefore requires constant refocussing of a microscope when scanning through the side of the tube to determine cell viability and cytopathology. The insert again provides an undesirably large surface area and, since plastic is itself fluorescent, is incompatible with a fluorescent microscope.
Yet another disadvantage is that cells grown in these three tubes cannot be directly centrifuged but must be transferred from the substrate on which they have grown. Another tube, the Shell vial, overcomes this problem because it is a vertical culture system having a flat bottom opposite the opening in the tube. The Shell vial contains a loose, unsecured 12 mm diameter glass coverslip which serves as the substrate for growing cells. As presently manufactured, however, the bottom of the glass vial is slightly thicker around its periphery, which creates an optical distortion making it diffcult to view cells through the bottom. Further, the plastic plug cap presently used to seal the Shell vial is thickened and of low optical translucence. Both of these features hinder determination of cell viability and cytopathology while the vial is sealed. More importantly, attempts to remove the coverslip can be exasperating and time consuming. Once removed, the loose cover slip is difficult to manipulate.
Another difficulty shared by the above culture tubes involves the culture medium which must surround the cells to ensure their viability. Unless the tubes are completely filled with culture medium, attached cells will dry out and die unless the proper orientation of the tube is maintained. This presents a severe problem during shipment, typically resulting in a 30% mortality rate of transported cell cultures.
In another art, there is a removable measurement partition which, when inserted in a specimen tube, quantifies the volume of a liquid sample. The "Click Stick," available from V-Tech, Inc., has a notch in the partition which accommodates a pipette for withdrawing liquid, such as a urine sample, held beneath the partition.